The present application claims priority to Japanese Patent Application No. 2000-185541 filed Jun. 21, 2000, the disclosure of which is incorporated by reference herein in its entirety.
The present invention relates to a mixed powder thermal spraying method, specifically to a mixed powder thermal spraying method in which a plasma jet is bent to carry out thermal spraying.
Techniques such as thermal spraying are widely used for sliding parts of cars as a method for providing sliding faces thereof with an abrasion resistance, and materials used for thermal spraying range over various fields from single materials to mixed (or combined) materials according to uses. Among them, a plasma thermal spraying gun for a bore is used when carrying out bore plasma thermal spraying as is the case with a bore internal surface for a cylinder block, and a structure of the plasma thermal spraying gun includes a system in which a plasma jet generated between an anode and a cathode is bent to an extension direction of the gun and thermally sprayed (FIG. 11) and a system in which a plasma jet is generated vertically to an extension direction of the gun according to arrangement of an anode and a cathode (FIG. 12).
An internal feeding method (a method in which powder is fed in the inside of a thermal spraying electrode) in which as shown in FIG. 11, powder 108 fed from a powder-feeding tube 106 passes through a powder-feeding passage 107 (pore) disposed in a copper alloy-made anode 102 and is fed to a plasma jet 104 from a feeding port 107a has so far been carried out as a method for feeding a powder material to a thermal spraying gun 101 having a system of bending a plasma jet.
When feeding a powder material by the system of FIG. 11, particles molten by the plasma jet 104 pass through the anode in the form of a thermal spraying flame 105, so that the molten particles 109 adhere to the inside of the anode (particularly the vicinity of a plasma jet injection port) in passing. If continuing thermal spraying as it is, adhesion of the molten particles 109 is expanded and comes to fill up the feeding port 107a, and the problem of clogging with the powder is brought about. Further, thermal spraying over a long period of time causes abrasion and deformation 107b of the powder-feeding passage 107 by virtue of flow of the powder. This causes turbulent flow in the powder-feeding passage 107 to reduce an injection speed of the powder, and therefore brought about is the problem that the molten particles 109 are liable to further adhere to the anode.
Accordingly, in such thermal spraying method, a frequency of maintenance of the thermal spraying gun against adhesion and clogging of the molten particles grows large, and the productivity is deteriorated. Further, when abrasion of the powder-feeding passage 107 is accelerated, the anode 102 has to be exchanged even if the anode 102 does not reach an intrinsic life. The anode 102 has a special shape and therefore is expensive, which has led to an increase in the product cost.
On the other hand, an external feeding method (a method in which powder is fed in the outside of the thermal spraying electrode) in which as shown in FIG. 12, powder 108 is fed to a resulting plasma jet 124 from a powder-feeding port 126a which is an outlet of a powder-feeding tube 126 has so far been carried out as a method for feeding a powder material to a thermal spraying gun 121 having a system in which a plasma jet is generated vertically to an extension direction of the gun.
In the system shown in FIG. 12, not only the thermal spraying distance is short as compared with the system shown in FIG. 11, but also the plasma output has had to be suppressed so that a heat effect is not exerted on an article to be processed. Accordingly, the plasma has a low output, and a very fine powder material has to be used in order to sufficiently melt and accelerate the powder material at a short thermal spraying distance, so that there have been the problems that the powder is increased in a cost and it is difficult to manage the powder. Further, the finer the powder is, the more the fluidity thereof is deteriorated, and therefore it is concerned that it becomes difficult to stably feed the powder.
In addition thereto, two kinds of the bore thermal spraying guns described above each have one powder-feeding port, and particularly when preparing a mixed thermal spraying film comprising two or more kinds of components, there has so far been employed, (1) a method in which plural powders to be used are mixed in advance and fed or (2) a method in which plural powders to be used are alloyed or combined (combination by mechanical alloy) in advance and fed.
In the method (1), it is difficult to continue feeding the mixed powders in an always fixed proportion. Further, there have been the problems that among the mixed powders, the powder having a lower melting point is molten before coming out from the powder-feeding port and liable to cause clogging and that if the plasma output is reduced in order to avoid it, the powder having a higher melting point is not sufficiently molten to reduce a quality of the thermal spraying film.
Further, in the method (2), there have so far been the problems that not only the powder cost is elevated but also alloying or combining is difficult because of the nature of the components of the material.
The present invention has been made in light of such existing situations, and an object thereof is to provide a mixed powder thermal spraying method in which an anode having a high durability and a low price can be used and a thermal spraying powder is easily managed and in which a thermal spraying film having a high quality is obtained.
In accordance with the present invention, there is provided a mixed powder thermal spraying method in which: a plasma jet is bent to carry out thermal spraying; in forming a mixed thermal spraying film comprising two kinds of materials having different melting points by bore thermal spraying, powder-feeding ports are provided for each material; and each powder-feeding port is controlled respectively to externally feed each material.
According to the method, the fed powder and the particles molten by a plasma jet do not pass through the inside of the anode, and therefore solved are the problems of adhesion of the molten particles to the anode, clogging of the fed powder caused by it and abrasion of a powder-feeding passage in the anode which have so far been brought about in conventional techniques. Accordingly, maintenance of the anode can be freed, and a life of the anode is extended. Further, the structure of the anode is simplified, so that the anode is decreased in a cost. Thus, the thermal spraying method which is excellent in a mass productivity and a maintenance can be provided at a low cost.
Further, the powder-feeding tube is a separate member, so that the feeding conditions are separately controlled in such a manner that the position of the feeding port can freely be set up, whereby the feeding conditions suited to the respective materials can be set up. A mixed proportion in the thermal spraying film can always constantly be maintained, and therefore a quality of the thermal spraying film is stabilized and elevated. Further, even if the powder-feeding tube is clogged, only the feeding tube can readily be exchanged.
To perform the mixed powder thermal spraying method in accordance with the present invention, it is advantageous to feed externally a material having a higher melting point from a thermal spraying flame high temperature part side and to feed externally a material having a lower melting point from a thermal spraying flame low temperature part side.
The plasma jet generated between the anode and the cathode in plasma thermal spraying stays in a very high temperature area. The powder is molten by the plasma jet, and the molten particles thereof form a thermal spraying flame. In thermal spraying, in order to efficiently melt the powder fed to form a thermal spraying film having less defects such as voids and a good quality, it is important to feed as much powder as possible to the plasma jet and apply sufficient heat to the powder. This requires to allow the powder-feeding port to be close to the plasma jet as much as possible to feed the powder. Supposing that the feeding port is kept away from the plasma jet, the powder injected from the feeding port spreads immediately after injected, so that the powder is less liable to reach the plasma jet and is not sufficiently heated and molten. As a result thereof, defects such as voids, inferior melting and inferior mixing are brought about in the film formed or brought about is the problem of a reduction in a yield (adhesion efficiency) of the powder, in which an amount of the powder introduced into the film is decreased as compared with the powder fed.
The present inventors have confirmed that in a bore plasma thermal spraying method in which a plasma jet is bent, the plasma jet after bent and the thermal spraying flame stay in a state in which the plasma jet is deviated and that a high temperature part and a low temperature part are present in the thermal spraying flame.
In this case, the powder-feeding port positioned in the high temperature part side of the thermal spraying flame is liable to be elevated to a high temperature, and when a material having a low melting point is fed to the plasma jet from the high temperature part side of the thermal spraying flame, the powder is molten at a temperature of the heated feeding port and clogs the vicinity of the feeding port, so that clogging is caused, and maintenance thereof is required. If the feeding port is kept away from the thermal spraying flame as a countermeasure therefor, a film having a good quality is not obtained as described above.
On the other hand, as shown in this embodiment, the powder material can sufficiently be molten by feeding the material having a high melting point from the powder-feeding tube in a high temperature part side of the thermal spraying flame to the plasma jet. Further, feeding of the material having a low melting point from the powder-feeding tube in a low temperature part side of the thermal spraying flame to the plasma jet makes it possible to bring the powder-feeding port close to the plasma jet while preventing clogging in the powder-feeding port, and therefore a thermal spraying film in which a melting state and a mixed proportion of the powder are stabilized and which has a good quality can be produced free of maintenance as well in mass production.
In the present invention, it is advantageous to set up 0xc2x0xe2x89xa6xcex11 and 0xc2x0xe2x89xa6xcex12, wherein xcex11 is an angle made by an injection direction of the powder fed from the thermal spraying high temperature part side to the plasma jet and a plasma jet-injecting face of an anode in a thermal spraying gun body, and xcex12 is an angle made by an injection direction of the powder fed from the thermal spraying low temperature part side to the plasma jet and the plasma jet-injecting face of the anode in the thermal spraying gun body.
With these features, 0xc2x0xe2x89xa6xcex11 and 0xc2x0xe2x89xa6xcex12 are set up, so that the particles do not adhere to the plasma-injecting face or the injection port in the anode, and the anode is free of maintenance. In this case, the powder fed is preferably brought close to the plasma jet-injecting port in order to sufficiently melt the powder, and as xcex11 and xcex12 grow large, the powder is less liable to be introduced into the plasma jet, so that the powder is insufficiently molten, and the yield is deteriorated. Accordingly, 0xc2x0xe2x89xa6xcex11xe2x89xa645xc2x0 and 0xc2x0xe2x89xa6xcex12xe2x89xa645xc2x0 are more preferred in order to prepare a film which is stable and has a good quality.
In the present invention, it is advantageous that another powder-feeding port is not present on an extension of the injection direction of the powder fed.
With this feature, another powder-feeding port is not present on an extension of the injection direction of the powder fed, so that the particles passing through the plasma jet and the flame do not adhere to the another powder-feeding port, and clogging is not brought about. Accordingly, the powder can continuously be fed free of maintenance.
In the present invention, it is advantageous that the material having a higher melting point is an Fe base material, and the material having a lower melting point is an Al base material and that the Fe base material is externally fed from the high temperature part side of the thermal spraying flame is externally fed to the plasma jet and the Al base material is externally fed from the low temperature part side of the thermal spraying flame to the plasma jet.
When a mixed powder of an Fe base material and an Al base material is thermally sprayed, they have so far been mixed or combined in advance, and in this case, the problems described in Prior Art have been brought about.
In the mixed powder thermal spraying method of the present invention, the Fe base material is fed to the plasma high temperature part, and therefore the Fe base material can sufficiently be molten. Further, the Al base material is fed to the plasma low temperature part, and therefore the Al base material can be prevented from being molten in the powder-feeding port more than required to bring about clogging.
Accordingly, the Fe base material and the Al base material can be fed on feeding conditions which are suited respectively to them, and therefore an Fe based-Al base mixed film in which the respective materials are sufficiently molten and mixed and which has a good quality can be prepared. Further, they are not mixed in the form of powders, so that an industrially special technique is not required, and it can be produced at a low cost.
The Fe base material includes, to be specific, white cast iron, carbon steel, Fexe2x80x94Mo base alloy, Fexe2x80x94Cr base alloy and Fexe2x80x94Ni base alloy, and the Al base material includes, to be specific, Alxe2x80x94Si base alloy, Alxe2x80x94Pb base alloy, Al-bronze alloy, Alxe2x80x94Cu base alloy and pure Al.